Scissors jack

ABSTRACT

A SCISSORS JACK HAVING A LOAD SUPPORTING MEMBER OPERATIVE TO BE RAISED AND LOWERED BY MOVEMENT OF A PAIR OF ADJUSTING ARMS TOWARD AND AWAY FROM EACH OTHER, A PAIR OF THREADED RODS INTERCONNECTING THE ARMS, AT SPACED POINTS. SPROCKETS MOUNTED ON EACH ROD AND A CHAIN DRIVINGLY INTERCONNECTING THE SPROCKETS.

Sept. 20, 1971 c, STEVENS 3,606,255

SCISSORS JACK Filed Aug. 1. 1968 FIGB INVENTOR. GQRDON C. STEVENS ATTORNEYS.

United States Patent 01 hoe 3,606,255 Patented Sept. 20, 1971 3,606,255 SCISSORS JACK Gordon C. Stevens, Garfield Heights, Ohio, assignor to The Chemical Rubber Company, Cleveland, Ohio Filed Aug. 1, 1968, Ser. No. 749,446 Int. Cl. 1366f 3/22 US. Cl. 254-122 3 Claims ABSTRACT OF THE DISCLOSURE A scissors jack having a load supporting member operative to be raised and lowered by movement of a pair of adjusting arms toward and away from each other, a pair of threaded rods interconnecting the arms, at spaced points, sprockets mounted on each rod and a chain drivingly interconnecting the sprockets.

This invention relates to the art of scissors jacks, and more particularly to an improved drive mechanism for the same.

The present invention is particularly applicable for use in fairly light duty, close tolerance positioning scissors jacks such as those used in scientific laboratories, and it will be described with particular reference thereto. However, it will be appreciated that the principles of the present invention have broader applications and may be used to advantage with scissors jacks designed for use in other environments.

The present invention contemplates improving a scissors jack which generally comprises a load supporting member, such as a platform, supported by two spaced sets of linkage, each compriing a parallelogram. The load supporting member or platform is elevated and lowered by conjointly lengthening and shortening a diagonal of each parallelogram.

This adjustment is accomplished by providing a pair of arms each extending perpendicularly between the spaced sets of linkage, and interconnecting one parallelogram with the other, at an apex defining a terminous of the diagonal to be lengthened or shortened.

In a conventional scissors jack, drive means are provided for moving the two adjusting arms toward and away from each other, whereby the aforementoined diagonal is lengthened or shortened, and the platform is correspondingly lowered or raised. In one commercial embodiment of such a scissor jack, the drive means takes the form of a single threaded rod, centered between the two spaced sets of linkage, and received in threaded apertures in the pair of adjusting arms. One end of the threaded rod is provided with a knob, handle or other suitable means to facilitate turning.

When the rod is turned in one direction, the two adjusting arms are brought toward each other, thereby elevating the platform. When the threaded rod is turned in the opposite direction, the two adjusting arms are caused to move away from each other, thereby lowering the platform.

Scissors jacks with the drive mechanism just described, operate quite satisfactorily when subjected to balanced loads up to the rated capacity of the jack, as well as when subjected to unbalanced loads which are small in relation to the rated capacity of the jack. However, smoothness of operation, and the levelness of ascension and descension deteriorate rapidly when an unbalanced load exceeds about 25% of the rated capacity of the jack. With heavier unbalanced loads, the linkage supporting the overloaded end of the platform tends to lag behind the other linkage during elevation and descent. This is due, apparently, to the unequal distribution of forces through the linkages, increasing the diagonal length in the overloaded linkage and correspondingly decreasing the diagonal length in the underloaded linkage. This disparity of diagonal lengths produces a torsional or twisting effect on the pivot of the linkages, thus increasing the overall frictional load. The increased frictional load causes the linkage bearing the greater load to lag behind the other linkage during ascent and descent, and makes the jack difficult to adjust. Moreover, a lagging in one linkage produces a tilt in the platform, which in turn throws the load out of level. This can cause serious problems, especially where the load consists of a container of liquid.

It follows from the foregoing discussion that there is a need for an improved scissors jack which is capable of handling efiiciently, unbalanced loads which are substantial in relation to the total capacity of the jack. The present invention is addressed to filling this need.

In accordance with the present invention there is provided, in a scissor jack having a load supporting member operative to be raised and lowered by the movement of a pair of adjusting arms toward and away from each other respectively; improved means for moving the adjusting arms comprising a first drive means operatively interconnecting the arms, and a second drive means operatively interconnecting the arms at points spaced from their interconnect with the first drive means, and transmission means interconnecting the first and second drive means, whereby force transmitted to one of the drive means is transmitted to the other of the drive means, and moving forces are thereby transmitted simultaneously by both drive means to spaced points along the adjusting arms.

It follows that in place of a single drive means centered between the two sets of linkage, the present invention provides a pair of parallel drive means, connected to each other, and connected to the adjusting arms for simultaneous movement. Thus, each set of linkage has its own drive means, operative in close proximity thereto. Consequently, an unbalanced load cannot produce the disparity of diagonal lengths which occur with a single drive means. Thus the improved drive means eliminates the torsional forces and their attedant increased frictional loads permitting level raising and lowering of the platform irrespective of the fact that the load borne by the platform may be an unbalanced one.

Another advantage of this arrangement is that it provides two means for applying input, which can be operated simultaneously, for example, with both hands. This makes it easier to raise and lower heavier loads, even when balanced.

It is therefore an object of the invention to provide a scissors jack of improved construction.

A further object of the invention is to provide a scissors jack which is capable of handling efiiciently unbalanced loads which are substantial in relation to the related capacity of the jack.

Still another object of the invention is to provide a scissors jack with improved means for moving a pair of adjusting arms toward and away from each other, comprising first and second interconnected drive means each of which is separately interconnected with the pair of adjusting arms at spaced points from each other.

These and other objects and advantages of the present invention will become apparent from the following de tailed description of a preferred embodiment of the invention, when read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic pictorial view of an improved scissors jack in accordance with the present invention;

FIG. 2 is a schematic plan view with parts cut away, of the scissors jack illustrated in FIG. 1; and

FIG. 3 is a schematic section view taken generally along line 3-3 of FIG. 2.

Referring now to the drawings wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same, FIG. 1 shows a scissors jack comprising a base 10, a load supporting member, which in the embodiment illustrated takes the form of platform 12 bearing load 14, and two spaced sets of linkage indicated generally as 16, 18 supporting platform 12 with respect to base 10.

Linkage 16 comprises a parallelogram made up of links 16a, 16b, 16c and 16d. Similarly, linkage 18 comprises a parallelogram made up of links 18a, 18b, 18c and 18d.

The scissor jack further comprises a pair of adjusting arms, 20, 22 extending perpendicularly between the spaced sets of linkage, and interconnecting one parallelogram with the other. Adjusting arms interconnects apex 24 of linkage 16 with apex 26 of linkage 18. Similarly, adjusting arm 22 connects apex 28 to linkage 16 with apex 30 of linkage 18; Apexes 24, 28, and 26, 30 define the termini of the diagonal of the parallelogram forming a portion of their respective linkages.

FIGS. 2 and 3 best show the means for moving arms 20, 22 toward and away from each other. These means comprise a first drive means designated generally as 32, and a second drive means designated generally as 34, and transmission means designated generally as 36.

In the embodiment illustrated, drive means 32 takes the form of threaded rod 38, and drive means 34 takes the form of threaded rod 40. Threaded rod 38 operatively interconnects arms 20, 22 by reception in threaded apertures in the arms.

Similarly, threaded rod 40 interconnects arms 20, 22 via threaded apertures at points spaced from the interconnect of the arms with rod 38. The threads at one end of rods 38, 40 are directionally opposite to the threads in the other ends of the rods. This same dilference of course applies to the corresponding threaded apertures in arms 20, 22. In this way, rotation of the rods in one direction causes the arms to move toward each other and rotation of the rods in the opposite direction causes the arms to move away from each other. It will thus be seen that separate drive means are positioned in close proximity to or in the plane of each of the pairs of linkages 16, 18. In the embodiment illustrated, transmission means 36 comprises a pair of sprockets '42, 44 suitably secured by splines (FIG. 3), or alternatively by keyways, set screws, pins and the like, to unthreaded portions 46, 48 respectively of threaded rods 38, 40'. The transmission means further comprises endless chain 50, drivingly interconnecting sprockets 42, 44.

The transmission means also includes means for maintaining threaded rods 38, 40 a fixed distance apart, thereby limiting variations in the tension in the endless chain 50. In the embodiment illustrated, this takes the form of bar 52, which is provided with openings near its distal ends, fitted with bushings 54, 56, which provide bearing surfaces for unthreaded portions 46, 48 respectively of threaded rods 38, 40. This arrangement ensures proper alignment of the threaded rods and their associated sprockets, with respect to each other and to the threaded apertures in arms 20, 22.

To facilitate turning threaded rods 38, 40, knobs 58, 60 are provided at one end of each rod.

Applying a turning force to one of the threaded rods, for instance rod 38, causes sprocket 42 to turn with the rod, which in turn causes chain 50 to rotate, together with sprocket 44 and threaded rod 40. At the same time, and depending upon the direction rod 38 is rotated, ad-

justing arms 20, 22 will move toward or away from each other, causing platform 12 to rise or lower respectively.

It will be appreciated that turning forces may be applied simultaneously to both knobs 58, 60, as well as to one or the other of the knobs.

Although the drive means have been illustrated in the preferred embodiment as threaded rods, and the transmission means as a chain and sprockets, it is to be understood that mechanical equivalents of these are also contemplated. Thus for example, rods 38, 40 may be replaced by worms operative against sectors formed integrally in arms 20, 22; sprockets 42, 44 may be replaced by pinions; and chain 50 may be replaced by a rack or worm.

Thus, the present invention has been described in conjunction With certain structural embodiments; however, it will be appreciated that various structural changes may be made in the illustrated embodiments without departing from the intended scope and spirit of the present invention as defined in the appended claims.

Having thus described my invention, I claim:

1. In a scissors jack comprising, a load supporting member, two spaced sets of parallelogram linkages connected to said member, adjusting means for conjointly lengthening and shortening a diagonal of each parallel ogram and thereby moving said load supporting member in opposite directions along a predetermined path, said adjusting means comprising a pair of arms each extend ing perpendicularly between said spaced sets of linkage and interconnecting one parallelogram with the other at an apex defining a terminus of said diagonal, a first drive means comprising a threaded rod having oppositely directed threaded ends received in correspondingly threaded apertures in said arms, a second drive means comprising a threaded rod having oppositely directed threaded ends received in correspondingly threaded apertures in said arms and spaced from the first mentioned apertures, first drive transmitting means non-rotatably connected to said first rod, second drive transmitting means non-rotatably secured to said second rod, said first and second drive transmitting means being connected to said first and second rods intermediate the ends of said rods and between said arms, transmission means drivingly interconnecting said first and second drive transmitting means whereby independent rotation of one of said rods relative to the other of said rods is prevented, and manually operable actuating means carried by each of said threaded rods.

2. The scissors jack as defined in claim 1 and including means intermediate the ends of said rods for maintaining alignment of said rods, said means for maintaining alignment of said rods comprising a rigid spacer member extending between and interconnecting said rods with said rods being rotatable relative to said spacer member.

3. The scissors jack as defined in claim 2 wherein each of said rods is provided with a non-threaded section with said non-threaded sections extending through nonthreaded apertures in said rigid spacer member.

References Cited UNITED STATES PATENTS 1,885,170 11/ 193 2 Anderson 25 4-9 2,624,535 1/1953 Bollhoefer 254-122X 3,384,349 5/ 1968 Johnson 2-54126- ROBERT C. RIORDON, Primary Examiner D. R. MELTON, Assistant Examiner 

